In recent years, nondestructive inspection techniques using a high-frequency electromagnetic wave of a millimeter-wave to terahertz-wave region (30 GHz to 30 THz) (hereinafter referred to as “terahertz wave”) have been under development. Various absorption lines of materials exist in a frequency range of the terahertz wave. Therefore, techniques expected in application fields of an electromagnetic wave of such a frequency band include an imaging technique using a safe fluoroscopic apparatus alternative to an X-ray apparatus, a spectral technique for obtaining an absorption spectrum or complex dielectric constant of a material to examine a bonding state therein, a technique for analyzing biomolecules, a technique for estimating a carrier concentration or mobility.
With respect to the biomolecular analyzing technique using the terahertz wave, there is an application example to a biosensor (Appl. Phys. Lett., Vol. 80, No. 1, p 154-p 156, 2002). As shown in FIGS. 17A, 17B, and 17C, the biosensor is produced by forming a resonance structure in a microstrip line waveguide. When an object (DNA) is applied to the resonance structure portion, the resonance frequency of the waveguide is shifted due to an interaction between the terahertz wave propagating through the waveguide and the object. Here, it is attempted to identify the object based on the amount of shift of the resonance frequency.
A structure in which an object holding portion is provided in a part of an optical waveguide to hold an object is disclosed as a sensor structure for analyzing the object (Japanese Patent Application Laid-Open No. 2001-074647). According to such a sensor, the property of the object is analyzed based on a change in a characteristic of a reflection light propagating through the optical waveguide at a boundary between the object and the optical waveguide. As shown in FIGS. 19A, 19B, and 19C, the object holding portion includes a groove pattern which is extended in a propagation direction and has a predetermined length.
The above-mentioned conventional techniques have the following problems.
FIG. 18 is a cross sectional model view showing a resonance structure portion formed by the method of forming the resonance structure in the waveguide. As shown in FIG. 18, a waveguide 1801 includes conductors 1803 and a ground conductor 1804, each of which is a metallic conductor, and a dielectric 1805 interposed therebetween. An electromagnetic field distribution 1806 in such an arrangement is shown in FIG. 18. Most electromagnetic waves are contained in the dielectric 1085. An object 1802 is analyzed in a region of leak-out of electromagnetic waves caused due to the proximity of the plurality of conductors 1803. As shown in FIG. 18, in order to analyze the object 1802, the object 1802 is applied to the waveguide 1801 so as to cover the entire resonance structure. However, as is seen from FIG. 18, the electromagnetic wave leak-out region, that is, a region in which the object 1802 interacts with the electromagnetic waves, is a minute region, so there is a problem that a part of the object 1802 which does not interact with the electromagnetic waves and is therefore unnecessary is large.
FIGS. 19A, 19B, and 19C are model views showing the sensor structure in which an object holding portion for holding an object is provided in a part of an optical waveguide. As shown in FIGS. 19A and 19B, in a sensor 1, an object 6 is held in an object holding groove 7 and a light is allowed to enter an optical waveguide as indicated by an arrow. The light propagating through the optical waveguide is reflected a plurality of times (two times in FIG. 19C) by the object 6. The object 6 is analyzed based on a change in the characteristic of the reflected light. However, as is also seen from FIG. 19C, the structure shown therein has a problem that a part of the object 6 which is not involved in the reflection of the light propagating through the optical waveguide by the object and is therefore unnecessary is large.
There have been increased demands on sensors for easily analyzing an object at the scene without using a special device and specialized knowledge which have been required up to now, such as an environmental analysis chip for analyzing substances contained in water, an atmosphere, or soil in outdoors scene and a health examination chip for easily performing a health examination at home. For easy analysis, the size of a sensor structure needs to be reduced and the minimum required amount of an object needs to be very small. Therefore, a sensor structure capable of effectively analyzing a small amount of an object has been required. In particular, when a living body is used as an object in the case of a health examination chip for performing a health examination at home, it is desirable that the analysis can be performed effectively with a smaller amount of the object in order to soften the resistance of a user.